Mesoderm induction is the first cell interaction in the amphibian embryo, and likely in other vertebrate embryos as well. Therefore the mechanism of this induction is of considerable interest. Members of two classes of growth factors are known to be effective in this event: fibroblast growth factor (FGF) and transforming growth factor beta (TGF-beta). We have shown that TGF-beta isoforms differ in their inducing capacity; earlier work identified TGF-beta2 as a mesoderm inducing factor while TGF-beta1 and beta5 are inactive. Recently we demonstrated that TGF-beta3 is a more potent inducer than other known TGF-beta isoforms. In addition we have confirmed the reports of others that activin A, a distant homolog of TGF-beta, is the most potent inducer identified so far. To study the mechanism of induction we isolated cDNA clones encoding the FGF receptor from Xenopus. FGF-R mRNA is present in early embryos when induction takes place, and disappears from uninduced ectoderm as it differentiates into epidermis. A nervous system-specific gene encoding a putative protein component of nuclear ribonucleoprotein complexes has been isolated and characterized. This gene, named nrp-1, is expressed in the developing brain of Xenopus tadpoles in the ventricular zone where cell proliferation takes place. We suggest that nrp-1 expression is required for the proliferation of cells in the nervous system. In a search for additional RNP protein genes in Xenopus we isolated a close relative of the nrp-1 gene, a relative of the ubiquitously expressed A1 hnRNP protein gene, and the frog homolog of the A2/B1 hnRNP protein gene. Tissue-specific RNP proteins may be involved in the differential control of RNA metabolism in development, and may thus be components of a system of gene regulatory mechanisms.